(a) Technical Field
The present disclosure relates to a planar microphone that is based on piezoelectric, electrospun poly (γ-benzyl-α,L-glutamate) (“PBLG”) nanofibers.
(b) Background Art
Since the first piezoelectric crystal microphone developed by A. Nicolson using Rochelle salt in 1919, piezoelectric materials have been widely used in various transducers. Low sensitivity and inconsistent frequency characteristics have traditionally limited the commercial use of such transducers for airborne sound. However, piezoelectric materials have found some use in underwater sound applications because these types of materials can operate over a wide range of static pressure.
Although the piezoelectric property of poly(vinylidene fluoride) (PVDF) first reported in 1969 stimulated interests in its use for transducers having a broad frequency range, low depolarization temperature (80° C.) limited its widespread use, while attempts to increase the depolarization temperature were met with only moderate improvements. In 1996, space charged low density polypropylene (LDPP) electrets were developed which exhibited large piezoelectric coefficient (>150 pC/N) equaling those in crystalline and ceramic materials. The mechanical properties and polarization of LDPP electrets have been extensively studied for applications in flexible field effect transistors, and ferroelectret accelerometers. Because fabrication of piezoelectric LDPP is relatively simple, it was once thought that this material could replace the crystal and ceramic materials used in microphones. However, the depolarization temperature (60° C.) of this material turned out to be even lower than that of PVDF and therefore could only be used under limited environmental conditions. Thus, there has been a long-standing need for improved piezoelectric materials that can be made into simple transducers and are also capable of working at high temperatures.